Studies in the Physiology of Parasitism. 
VI. Infection by Sclerotinia Libertiana. 
BY 
C. BOYLE, B.Sc. (Lond.), A.R.C.S.I. 
(The Department of Plant Physiology and Pathology , Imperial College of Science and 
Technology , South Kensington .) 
With Plate XIV. 
HE earliest investigations on the parasitism of Sclerotinia Libertiana 
-L are those of de Bary (4), who studied the infection of the host plant 
from ripe ascospores placed in drops of nutrient solution and in pure water 
respectively. In the former case the spores germinated and produced 
a vigorous mycelium which at once penetrated into the living healthy tissue 
of the plant and killed it. When, however, germination took place in pure 
water, the germ tubes produced were quite unable to penetrate into the 
living tissue. De Bary concluded that ‘ the power of infecting is shown by 
the power of penetrating the membranes, which are evidently dissolved at 
the points of penetration. Hence it is very probable that this power 
depends on the presence of a substance which can dissolve a membrane, 
a ferment in fact, and that this substance is not formed and discharged in 
sufficient quantity till the germ tube from the spore is properly nourished 
and developed.’ The hypothesis that parasitic fungi which are not wound 
parasites are capable of secreting a ferment which softens and dissolves 
cuticle appears to have been generally accepted by the earlier workers. 
In his classical investigations on the lily disease caused by Botrytis, 
Marshall Ward (10) expressed the opinion that the germ tube of the fungus 
dissolved the cuticularized epidermal wall of the host. Busgen (3), while 
discussing the importance of appressoria in bringing the fungus and host 
into close contact, assumed that the function of these organs was to serve 
for the accumulation and penetration of toxic material into the host plant. 
Voges (14) supposed that the mucilage surrounding the spores of Fusi- 
cladium , in addition to functioning as an adhesive substance, softened and 
dissolved the cuticle and thus facilitated the penetration of the germ tube. 
Miyoshi (i 1) postulated the existence of chemotropic stimuli and emphasized 
[Annals of Botany, Vol. XXXV. No. CXXXIX. July, 1921.] 
